Fluid is commonly pumped though tubing inserted into a well to drill or to provide intervention services such as stimulation or milling of obstructions. Means for pulsing this flow have been developed for a variety of applications, including mud pulse telemetry, well stimulation, enhanced drilling, and for use in extending the lateral range of drilling motors or other well intervention tools. For example, U.S. Pat. Nos. 6,237,701 and 7,139,219, which are assigned to the same assignee of the present invention, disclose hydraulic impulse generators incorporating self-piloted poppet valves designed to periodically stop the flow of fluid at the bottom end of the tubing. Stopping the flow leads to an increase in pressure upstream of the valve and a decrease in pressure downstream of the valve. U.S. Pat. No. 6,237,701 describes a self-piloted self-cycling valve that creates water hammer pulses near the end of a drill string and suction pulses in the borehole. This pulse valve is envisioned to improve rate of penetration (ROP) and produce useful seismic waves while drilling.
U.S. Pat. No. 8,528,649 describes a similar pulse valve, but with improved pulse control. This valve incorporates a flow restriction that creates a differential pressure to drive valve actuation. Bypass passages can be added to reduce the intensity of the water hammer pulses as desired. These pulse valves are known to greatly improve lateral reach (effectively reducing friction coefficient) and improve weight transfer to the bit in coiled tubing purveyed applications. Additional benefits for directional drilling applications can include a reduction of stick-slip tubing behavior and improved tool face alignment.
Each of the devices described in the above-mentioned patents utilize cylindrical sliding clearance seals to isolate various annular cavities from one another. These clearance seals must have precise manufacturing tolerances in order to control leakage between the annular cavities. The usable life of the components that incorporate these clearance seals is limited primarily due to surface damage and wear caused by erosion. Hard, wear and erosion resistant materials can be used to prolong usable wear life, but longer wear life is desirable.
Drilling is normally done with sections of jointed tubing (drill pipe). Wells are routinely drilled to measured depths that exceed 15,000 ft. Since it takes significant time and effort to traverse the bottomhole assembly out of and into a wellbore of such a depth, best overall drilling efficiency is achieved by maximizing the length of runs. Drill bits, downhole motors, and other downhole components need to be able to survive at least 100 hours to be generally acceptable. Longer runs of as much as 200 hours are desirable.
It is also well known that when drilling mud experiences turbulence due to high velocity and or abrupt changes in direction, erosion will cause localized damage to components. The rate at which wear and damage occurs is primarily affected by localized velocities, abrasive solids content in the fluid, and material hardness. The fluid pumped down a drill pipe during drilling (drilling mud) contains bentonite and usually barite. Bentonite is a gelling agent that keeps relatively large particles in suspension. Barite is a weighting agent that increases the density of the fluid. Barite is comprised of tiny particles (up to 0.003″) that are quite hard and abrasive. Fluid is normally pumped down the drill pipe, up the wellbore, and collected near the well at the surface. Fluid is normally cleaned using a variety of well-known means and recirculated through the system. Cuttings from the well such as sand and small rock fragments tend to stay in suspension and are usually even harder and more abrasive than the barite.
The presence of clearance seals, abrasive materials such as barite, and the need to continue to be effective for long periods of operation make for a very challenging combination of conditions for downhole pulse valves. The self-cycling pulse valves of the type described in the patents referenced above create a differential pressure that provides the motive force to operate. An orifice or Venturi is incorporated that partially restricts the primary flow path. The portion of the pulse valve cycle in which the clearance seals experience the highest differential pressure is while the valve is closed and the water hammer is occurring. The differential pressure across the valve during that period of time can be roughly ten times that which exists when the valve is open. Actuation does not require such a high pressure; it is merely the natural consequence of the water hammer operation.
It would thus be desirable to provide an apparatus and method for reducing the differential pressure through the internal passages and clearance seals primarily during the water hammer pulse. One benefit of such a solution would be to increase usable wear life of internal components for drilling application. Another benefit may include increasing controllability of the pulse duration with larger clearances than earlier devices provided. This can allow for longer duration pulses which are desirable. One alternative application of this invention can include self-piloted pulse valves used in non-drilling downhole applications.
Pressure pulsations in the tubing disposed upstream of the bottom hole assembly (BHA) can provide a plurality of beneficial effects. For example, the pulsations can improve the performance of rotary drilling by applying a cyclical mechanical load on the bit and a cyclic pressure load on the material that is being cut. In combination, these loads can enhance cutting. The vibrations induced by these cutting tools in the tubing can reduce the friction required to feed the tubing into long wells that deviate from a straight bore line.
The self-piloted poppet valve also generates pressure fluctuations in the wellbore near the tool. These pressure fluctuations can enhance chemical placement in the formation and enhance the production of formation fluids, such as oil or gas. In addition, the pressure pulses can also be used to generate a signal that can be employed for seismic processing. The pulses can be tuned to be an impulse with a cycle period longer than 1 second. This type of pulse is preferred for seismic interpretation, because the travel times of seismic waves in the earth crust for formations of interest, such as oil-and gas production, are on the order of seconds. The long period energy generated by this type of cyclic impulse that is produced by the present exemplary pulse valve also propagates long distances in the earth and is ideal for pore pressure prediction
It would thus be desirable to provide an apparatus and method that allows for the reduction of differential pressure through the internal passages and clearance seals for pulse valves used in downhole applications, as compared to the differential pressure generated by existing pulse valve designs.